Home evolved Node Bs (H(e)NBs) and Home Node Bs (HNBs) (collectively referred to as HNBs) have been introduced in long term evolution (LTE) and Universal Mobile Telecommunications System (UMTS), respectively, as part of an effort to provide improved spectral efficiency, reduced latency, and better utilization of radio resources for faster user experiences, richer applications and lower cost services. The HNB provides subscribers with access to network services over extremely small service areas, such as homes or small offices. A subscriber (e.g., an individual or an organization) may deploy a HNB over an area where such service is desired. An HNB closed subscriber group (CSG) cell is a defined area over which radio coverage provided by the HNB may only be accessed by a group of subscribers authorized to use the services of the cell. HNBs may be deployed on the same carrier as open or macro base stations. This may be referred to as “mixed carrier deployment”. HNBs may also be deployed in a dedicated carrier.
A open cell may have the possibility of signaling an “intra-frequency reselection indicator” (IFRI) that indicates to the neighboring wireless transmit/receive units (WTRUs) whether they are allowed to stay camped on another cell that uses the same frequency in case the open cell is barred. In order to prevent excessive interference with the barred cell when the WTRU initiates communication with a neighbor cell on the same frequency, the IFRI may be set to “not allowed”. This forces the WTRUs for which the barred cell is best ranked, to camp on another frequency. However, a WTRU may not obey the IFRI transmitted from a CSG cell in order to prevent an excessive number of reselections to other frequencies in dense HNB deployments. A WTRU is not allowed to camp on a CSG cell which is not suitable for the WTRU (i.e., the WTRU is not member of a CSG cell).
When the frequency used by both the open base stations and HNBs is set as the highest priority by the network, a WTRU may camp on a cell on this frequency as long as the signal strength or quality is above a threshold. Accordingly, a WTRU located in an area of densely deployed HNBs may find itself in a situation where the best ranked cell from signal strength (or quality) point-of-view is a CSG cell, but this CSG cell is not suitable because the WTRU is not a member of this CSG. However, since the WTRU ignores the IFRI indicator from this CSG cell it would stay camped on an open cell on the same frequency. At the time of initiating communication with the network, the WTRU is likely to be heavily interfered with by the CSG cell if the CSG cell is heavily loaded. As a result, service at this location will be denied for the WTRU.
In one proposed solution, the WTRU should obey the IFRI indication from the CSG cell for a certain amount of time. This solution, however, results in a large number of cell reselections to other frequencies. In another solution, the WTRU would only be allowed to stay camped on the open cell if it is sufficiently close to the CSG cell. In the proposed solutions, the WTRU would be denied service if no other cell is available on another frequency. These issues may be addressed by implementing methods for avoiding interference from HNB transmissions from the CSG cell when the WTRU is moving through a dense deployment of HNBs.